Unit for cooling a film made of synthetic material

ABSTRACT

The invention relates to a cooling unit ( 2 ) which comprises a cooling tank ( 3 ) at least partially filled with a heat transport coolant, and a cooling drum ( 4 ) at least partially submerged in the cooling tank, the cooling drum including a shell ( 5 ) having two side flanges ( 6 ) which are at least partially perforated such that the inside of the shell is at least partially filled with the heat transport coolant. The cooling tank ( 3 ) comprises at least one heat transport coolant supply opening ( 12 ) situated opposite one of the side flanges ( 6 ) of the shell ( 5 ) and designed to supply the cooling tank with the heat transport coolant.

TECHNICAL FIELD

The present invention relates to a cooling unit for a film in synthetic material, and preferably a film in a biaxially oriented (bi-oriented) synthetic material.

BRIEF DISCUSSION OF RELATED ART

Bi-oriented synthetic material films are obtained from an extruded ribbon, after having deposited the molten material (polypropylene, polyester, polyamide, PVC, etc.) on a casting drum, or a cooling drum, cooled by circulation of fluid so as to slow down the crystallization of the film and to allow its subsequent drawing.

The extruded ribbon, cooled in a cooling tank after its passing over the casting drum, then passes into a longitudinal drawing machine equipped with preheating cylinders intended to heat up the ribbon to the drawing temperature, and with a train of cylinders driven at different rates and intended to longitudinally draw the ribbon.

The ribbon thereby drawn in its longitudinal direction then penetrates into a transverse drawing machine which includes two groups of nips which respectively take the ribbon of both of its sides, both groups of nips being mounted on chains, the spacing of which increases gradually until it attains the desired width.

When this drawing operation has been performed, a suitable device opens the nips and allows the thereby formed film to be transferred, after cooling on a set of cylinders, to a winding device at which the film is wound on a storage roll.

A cooling unit formed by a cooling drum and a cooling tank presently requires the use of a cooling unit producing water at a temperature from 10 to 11° C. intended to feed a water/water exchanger which allows the temperature of water circulating in two different circuits, one feeding circulation internal to the casting drum, the other one feeding circulation internal to the cooling tank to be maintained at a temperature of 35° C.

The internal circulation to the casting drum is achieved, in the present state of the art, by circulation of water inside helical channels, either crossed or not, extending along the internal face of the casting drum, or by using water jets projecting water on the internal face of the latter.

In order to obtain a film in a synthetic material which may be transformed subsequently under optimum conditions, it is essential that the cooling drum have very large regularity of temperature over the whole of its surface intended to be in contact with the film on the one hand and ensure rapid cooling of the latter on the other hand.

Consequently, the circulation internal to the casting drum requires significant flow rates, therefore the use of high power pumps which consume energy considering the complexity of the circuit which provides exchanges, filters, rotating joints, etc. and which involves high pressure drops.

The circuit internal to the cooling tank provides, in the present state of the art, significant circulation of amounts of water generally injected into the cooling tank by means of ramps which have significant pressure drops and also require the presence of energy-consuming pumps.

Thus, such a cooling unit is therefore highly consuming in energy, not only at the cold unit but also at the circulation pumps required for operating the cooling circuits.

BRIEF SUMMARY

The present invention aims at finding a remedy to these drawbacks.

The technical problem at the basis of the invention therefore comprises providing a cooling unit which is of a simple structure and which allows reduction in significant proportions of the energy expenditures required for producing a film in synthetic material.

For this purpose, the present invention relates to a cooling unit for a film in synthetic material, including:

-   -   a cooling tank at least partly filled with a heat transfer         liquid, and     -   a cooling drum at least partly immersed in the cooling tank,

characterized in that the cooling drum comprises a shell having two lateral flanges at least partly openworked so that the inside of the shell is at least partly filled with the heat transfer liquid, and in that the cooling tank includes at least one heat transfer liquid supply mouth laid out for supplying heat transfer liquid to the cooling tank, said at least one heat transfer liquid supply mouth being located facing one of the flanges of the shell.

The fact that the cooling drum is immersed in the cooling tank and that the inside of the shell directly soaks in the heat transfer liquid contained in the cooling tank allows, because of the stirring of the heat transfer liquid volume comprised inside the shell of the drum during its rotation, homogenization of the temperature of the large volume of heat transfer liquid contained inside the shell, therefore easily providing homogeneity in temperature on the whole of the outer face of the drum.

Further, because of its positioning facing one of the flanges of the shell, at least one supply mouth is laid out so as to feed with heat transfer liquid the inside of the shell of the drum, which further promotes stirring of the heat transfer liquid volume comprised inside the shell, and therefore homogenization of the temperature of this heat transfer liquid volume.

Further, because of the structure of the assembly according to the invention, a single circuit, and therefore a single pump, are required for introducing the heat transfer liquid inside the drum, and in the same way inside the cooling tank.

Therefore, when the cooling unit according to the invention is set into place on a production line with great capacity, a significant reduction in the consumed energy by the production line is achieved.

Preferably, at least said one supply mouth is laid out for feeding with heat transfer liquid the inside of the shell of the drum and the cooling tank simultaneously.

Advantageously, the heat transfer liquid contained in the cooling tank is water.

Further, the unit according to the invention allows the use of a drum without any circulation channels, and of spray devices, with which the manufacturing costs of the drum may be reduced.

Preferably, the unit includes a retention tank and a heat transfer liquid circulation circuit comprising at least one conduit for supply a heat transfer liquid, connecting the retention tank to the cooling tank and laid out for supplying heat transfer liquid to the cooling tank, and at least one return conduit connecting the cooling tank to the retention tank and laid out for discharging the heat transfer liquid contained in the tank to the retention tank.

Advantageously, the retention tank is positioned below the cooling tank. Thus, the heat transfer liquid intended to feed the cooling drum/cooling tank unit is taken from the retention tank located immediately below the unit, therefore in proximity to the latter. The result of this is an extremely simple circuit without any unnecessary pressure drop, without any rotating joint, and therefore only requiring a pump with low energy consumption.

Advantageously, the unit includes a refrigerating unit laid out for cooling a heat transfer fluid, and at least one coil positioned in the retention tank and the ends of which are connected to the refrigerating unit so that said heat transfer fluid may circulate in said coil. These arrangements allow efficient and simple cooling of the heat transfer liquid intended to feed the cooling tank.

The heat transfer fluid according to one embodiment is Freon.

Advantageously, the circuit for circulating a heat transfer liquid includes a pump laid out for supplying a heat transfer liquid to said at least one supply mouth.

It should be noted that the inner wall of the shell may have surface roughness, and be provided with a plurality of fins distributed over its surface, and preferably regularly distributed over its surface. Advantageously, the shell is made in a metal having a high thermal conductivity coefficient. With these arrangements, it is possible to improve the efficiency of the heat transfer between the inner face of the extruded ribbon and the water contained inside the shell of the drum.

Advantageously, the unit includes rotary driving means, laid out for driving the shell into rotation around a substantially horizontal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

Anyway, the invention will be better understood by means of the description which follows with reference to the appended schematic drawing representing as a non-limiting example, an embodiment of this cooling unit.

FIG. 1 is a schematic side view of a cooling unit according to the invention.

FIG. 2 is a schematic sectional view of the cooling unit of FIG. 1.

FIGS. 1 and 2 illustrate a unit 2 for cooling a film in synthetic material.

DETAILED DESCRIPTION

Such a cooling unit 2 is more particularly intended to be integrated into a production line for a film in synthetic material and to be positioned between an extruder and drawing equipment of such a production line.

As shown in the figures, the cooling unit 2 includes a cooling tank 3 partly filled with a heat transfer liquid, such as water, and a cooling drum 4 partly immersed in the cooling tank 3.

The cooling drum 4 comprises a shell 5 having two lateral flanges 6 partly openworked so that the inside of the shell 5 is partly filled with the heat transfer liquid contained in the cooling tank 3.

As shown more particularly in FIG. 1, the cooling drum 4 is positioned below a die 7 for shaping an extruded ribbon 8 intended to be cooled by the cooling drum 4.

The shell 5 is advantageously made in a metal having a high thermal conductivity coefficient. The inner wall 9 of the shell preferably has surface roughness, and may also be provided with a plurality of fins distributed over its surface, and preferably regularly distributed over its surface.

The cooling unit 2 includes rotary driving means, laid out in order to drive the shell 5 into rotation around a substantially horizontal axis. The rotary driving means preferably include two coaxial shafts 11, each connected to one of the flanges 6 of the shell, and at least one driving motor (not illustrated in the figures) coupled with one of the shafts.

The cooling tank 3 includes two mouths 12 for feeding heat transfer liquid, laid out in order to supply a heat transfer liquid to the cooling tank. Each heat transfer liquid supply mouth 12 is advantageously located facing one of the flanges 6 of the shell 5.

The cooling unit 2 further comprises a retention tank 13 positioned below the cooling tank 3, and a circuit for circulating a heat transfer liquid 14 connected to the cooling 3 and retention 13 tanks. The circuit for circulating a heat transfer liquid 14 comprises two conduits for feeding a heat transfer liquid 15 each connecting the retention tank 13 to the cooling tank 3 and laid out in order to supply heat transfer liquid to the cooling tank 3, and two return conduits each connecting the cooling tank 3 to the retention tank 13 and laid out in order to discharge the heat transfer liquid contained in the cooling tank to the retention tank.

The cooling unit 2 also includes a refrigerating unit 17 laid out for cooling a heat transfer fluid, and two coils 18 positioned in the retention tank 13 and the ends of which are connected to the refrigerating unit 17 so that said heat transfer fluid may circulate in both coils.

It should be noted that the circuit for circulating a heat transfer liquid 14 includes a pump laid out for feeding heat transfer liquid to both heat transfer liquid supply conduits 15 and both supply mouths 12.

As this is obvious, the invention is not limited to the single embodiment of this cooling unit, described above as an example, it, on the contrary, encompasses all the alternative embodiments. 

1. An assembly for cooling a film in synthetic material, comprising: a cooling tank at least partly filled with a heat transfer liquid, and a cooling drum at least partly immersed in the cooling tank, wherein the cooling drum comprises a shell having two lateral flanges at least partly open-worked so that an inside of the shell is at least partly filled with the heat transfer liquid, and wherein the cooling tank includes at least one mouth for feeding a heat transfer liquid, laid out for feeding the cooling tank with a heat transfer liquid, said at least one heat transfer liquid supply mouth being located facing one of the flanges of the shell.
 2. The assembly according to claim 1, further comprising a retention tank and a circuit for circulating a heat transfer liquid comprising at least one heat transfer liquid supply conduit connecting the retention tank to the cooling tank and laid out in order to feed the cooling tank with heat transfer liquid, and at least one return conduit connecting the cooling tank to the retention tank and laid out in order to discharge the heat transfer liquid contained in the cooling tank into the retention tank.
 3. The assembly according to claim 2, wherein the retention tank is positioned below the cooling tank.
 4. The assembly according to claim 2, further comprising a refrigerating unit laid out in order to cool a heat transfer fluid, and at least one coil positioned in the retention tank and the ends of which are connected to the refrigerating unit so that said heat transfer fluid may circulate in said coil.
 5. The assembly according to claim 2, wherein the circuit for circulating a heat transfer liquid includes a pump laid out for feeding with heat transfer liquid at least one supply mouth.
 6. The assembly according to claim 1, wherein the inner wall of the shell has surface roughness.
 7. The assembly according to claim 1, wherein the inner wall of the shell is provided with a plurality of fins distributed over the surface.
 8. The assembly according to claim 1, wherein the shell is made in a metal having a high thermal conductivity coefficient.
 9. The assembly according to claim 1, wherein the cooling drum is immersed in the cooling tank so that the liquid level in the cooling tank is located above the axis of rotation of the cooling drum.
 10. The assembly according to claim 7, wherein the plurality of fins are regularly distributed over the surface. 